The present invention relates to systems for illuminating a desired area with electromagnetic radiation, such as visible or infrared light, with a desired intensity distribution, using a combination of direct radiation over a portion of the desired area together with constructive occlusion to fill in other regions of the desired area. In one type of visible lighting system, for example, an embodiment of the invention uses direct illumination to provide relatively high intensity illumination in regions near the system horizon for a full circle around the system. The exemplary embodiment utilizes principles of constructive occlusion to provide a lower intensity illumination for higher elevation regions up to the vertical axis of the system.
Radiant or electromagnetic energy emitters and distributors find a wide range of applications in modern society. Visible illumination systems, for example, illuminate areas and surfaces to enable use by personnel even though natural ambient lighting might be insufficient. Infrared illumination is a critical component of many night-vision technologies. Other lighting devices provide guidance or warnings, for example to enable pilots to locate the edges of runways or taxiways, to illuminate emergency exit paths, to visibly indicate the emergency, etc.
Different applications of radiant energy illumination systems require different performance characteristics. For example, a visible illumination application might require that the lighting system provides a desired minimum intensity over a flat surface of specified dimensions about an axis of the lighting system, at a known distance from the system along its axis. Simple radiation sources, such as light emitting diodes (LEDs) or light bulbs with reflectors and/or lenses typically provide a high intensity radiation in regions close to the axis, but the intensity drops of quickly at angles approaching the horizon. On an illuminated surface, the intensity is not uniform. To provide a desired illumination at edges of a design footprint, the source often will emit substantially higher amounts of radiation than necessary along the axis.
Prior attempts to provide desired intensity distributions have involved complex arrangements of sources, lenses and reflectors. These complex arrangements tend to be relatively expensive and sensitive to problems of misalignment, which limits ruggedness and durability.
As another example of a difficult lighting application, consider an airport lighting system. The regulatory authority requires a high intensity illumination for regions near the horizon, such as from the horizon up to an elevation of about 6xc2x0. The airport light must also emit some light at higher elevations, including along the vertical axis; however, the intensity required at higher elevations may be an order of magnitude lower than that near the horizon. Existing blue taxiway lights and other runway lights utilize conventional light-bulb technologies. Such lamps do meet the requirement for illumination at the horizon as well as illumination above, although they tend to over illuminate areas at high elevations above the horizon, in order to provide adequate intensity at all necessary angles. As such, they tend to consume more power than is necessary. More importantly, the lamp burns out and must be replaced every 2000 hours or so.
Efforts are underway to develop a runway/taxiway lighting system utilizing LEDs, because of the long life of such light sources (hundreds of thousands of hours). However, to achieve the necessary coverage with adequate intensity, LED-based systems have used a complex matrix with a large number LEDs. For example, horizontal LEDs might irradiate low elevation regions, but additional sets of LEDs directed to higher elevations and one or more vertically directed LEDs are needed to fill-in various portions of the field of illumination. Examples of such systems have included as many as 40-60 LEDs. As a result, the LED-based system becomes quite expensive to construct and draws an inordinate amount of electrical power.
U.S. Pat. No. 5,733,028 issued Mar. 31, 1998 to Ramer et al. discloses a number of embodiments of illumination systems that utilize constructive occlusion. With this technology, a mask occludes an active optical surface, typically a Lambertian surface formed by the aperture of a diffusely reflective cavity, in order to distribute radiant energy with a tailored intensity distribution. The disclosure there emphasizes uniformity of the intensity distribution, for example with respect to angles extending over a hemispherical radiation pattern. Adjustment of the parameters of the constructive occlusion system enables the system designer to tailor the system performance to a wide range of applications. Constructive occlusion typically emphasizes distribution based on multiple diffuse reflections within a mask and cavity system. Careful selection of the system parameters can adapt the constructive occlusion system to meet the requirements of many diverse illumination applications.
However, a need still exists for radiant energy or electromagnetic emission and distribution systems, which can satisfy certain extreme requirements in differences in intensity distribution. Such systems must be relatively simple in structure, to minimize cost and maximize durability. Also, such systems should be able to achieve a desired intensity distribution, with large variations in power at different angles of illumination, without requiring excessive input power or over illumination at any particular angle, to thereby maximize efficiency.
To meet the above stated needs and objectives, the inventions combine direct illumination from a source with illumination provided by constructive occlusion techniques. Such a combination of different types of illumination can precisely satisfy design requirements of more than an order of magnitude difference in illumination intensities in different segments of an intended region of illumination. The direct illumination from the source provides high intensity illumination for certain desired regions. Some radiant energy from the source also diffuses and reflects between the mask and cavity of the constructive occlusion system. The parameters of the mask and cavity are such that radiant energy processed by those elements provides a tailored intensity distribution, including a predetermined low intensity illumination in a region not covered by the direct illumination.
In one aspect, the inventions relate to systems for projecting electromagnetic radiation, such as visible light. Such a system includes a base having a first defined area substantially facing a region to be illuminated with the electromagnetic radiation. This area of the base has a reflective characteristic with respect to the electromagnetic radiation. The system also includes a mask. The mask is positioned between the base and the region to be illuminated at a predetermined distance from the defined area of the base. The mask also has a defined area, substantially facing the area on the base, which has a reflective characteristic with respect to the electromagnetic radiation. One of the defined areas has a cavity. The inner surface of the cavity has a substantially diffuse reflective characteristic with respect to the electromagnetic radiation. The mask occludes electromagnetic radiation emerging from an aperture of the cavity. The inventive system also includes a source. The source emits a substantial first portion of the electromagnetic radiation directly into a predetermined section of the region to be illuminated. The source also emits a substantial second portion of the electromagnetic radiation into the cavity. The direct radiation provides a relatively high intensity illumination in the predetermined section, whereas the base, mask and cavity provide a tailored intensity distribution of the second portion of the electromagnetic radiation over another predetermined section of the region to be illuminated.
The second portion of the electromagnetic radiation provides a relatively low intensity illumination over at least a portion of the second illuminated section. Many applications of the system actually provide an intensity of the direct illumination that is an order of magnitude higher than the lowest desired intensity in the section of tailored illumination covered by the constructive occlusion.
Several of the preferred embodiments provide the low intensity illumination in regions about an axis of the mask and cavity system. In such cases, the direct, high intensity illumination covers angles relatively far-off the axis. For example, the system may provide the high intensity at angles directed towards distant edges of a wide planar surface, which is uniformly illuminated by the system. Other exemplary embodiments provide the high intensity illumination at angles approaching the system horizon.
The inventive system may utilize a variety of reflective materials. Preferred embodiments utilize materials providing diffusely reflective surfaces on the elements of the constructive occlusion system. The preferred embodiments of the mask and cavity system also include a reflective shoulder, formed around a portion or around the entire aperture of the cavity. The system may also include a reflective baffle, in the region between the mask and the cavity surface, to reflect additional light into certain regions of the desired field of illumination, typically at relatively large angles with respect to the axis of the mask and cavity.
Another inventive aspect relates more specifically to an airport lighting system, designed to meet the particular requirements for airport lighting. This system includes a cavity with a diffusely reflective inner surface. A reflective shoulder surrounds at least part of the aperture of the cavity. The system also includes a mask. The mask is outside the cavity at a distance from the aperture, between the aperture and a region to be illuminated. The surface of the mask facing toward the aperture is reflective. The system also includes a source of radiant light energy. The source is positioned between the mask and the aperture, for example near the reflective surface of the mask. The mask is sufficiently spaced from the aperture of the cavity such that the source directly emits a substantial first portion of its radiant light energy into a region adjacent to a horizon of the system. This direct emission provides a relatively high intensity illumination. The source emits a second portion of its radiant light energy into the cavity. The reflective surface of the mask constructively occludes the aperture of the cavity, so that the system radiates the second portion of the radiant light energy into a region at higher elevations above the horizon, but with a relatively lower intensity distribution.
Such an airport lighting system can efficiently provide high intensity illumination near the horizon, for example, from the horizon up to angles of at least 6xc2x0. Such systems also efficiently satisfy the requirements for lower intensity illumination at higher elevation angles. A preferred embodiment utilizes LEDs as the light source. Such embodiments typically include a series of LEDs arrange in a ring, with the LEDs facing outward to radially emit the direct illumination energy into the regions near the horizon. The inventive system utilizes far fewer LEDs, when compared to prior attempts to provide airport lighting using LEDs. Consequently, the cost of the system as well as the power consumption (one cost of operating the system) are much lower.
Another inventive aspect relates to a system for projecting electromagnetic radiation with a tailored intensity distribution. The distribution includes a high intensity portion in a first angular region of an area to be illuminated and a low intensity portion in a second angular region of the area to be illuminated. This system includes a diffusely reflective cavity with an aperture. A mask outside the cavity constructively occludes the aperture with respect to at least the second angular region. The mask has a reflective surface facing toward the aperture. The mask and cavity provide the low intensity portion of the illumination distribution. The inventive system also includes means for directly illuminating the first angular region with electromagnetic energy to provide the high intensity portion of the illumination distribution and for supplying electromagnetic radiation into the cavity.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.